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Structural Design Challenges of Shanghai Tower
Author: Yi Zhu
Affiliation: American Society of Social Engineers
Street Address: 398 Han Kou Road, Hang Sheng Building
City: Shanghai
State/County:
Zip/Postal Code: 200001
Country: People’s Republic of China
Email Address: [email protected]
Fax: 1.917.661.7801
Telephone: 011.86.21.6057.0902
Website: http://www.thorntontomasetti.com
Author: Dennis Poon
Affiliation: Council on Tall Buildings and Urban Habitat
Street Address: 51 Madison Avenue
City: New York
State/County: NY
Zip/Postal Code: 10010
Country: United States of America
Email Address: [email protected]
Fax: 1.917.661.7801
Telephone: 1.917.661.7800
Website: http://www.thorntontomasetti.com
Author: Emmanuel E. Velivasakis
Affiliation: American Society of Civil Engineers
Street Address: 51 Madison Avenue
City: New York
State/County: NY
Zip/Postal Code: 10010
Country: Unites States of America
Email Address: [email protected]
Fax: +1.917.661.7801
Telephone: +1.917.661.8072
Website: http://www.thorntontomasetti.com
Author: Steve Zuo
Affiliation: American Institute of Steel Construction; Structural Engineers Association of New York;
American Society of Civil Engineers
Street Address: 51 Madison Avenue
City: New York
State/County: NY
Zip/Postal Code: 10010
Country: United States of America
Email Address: [email protected]
Fax: 1.917.661.7801
Telephone: 1.917.661.7800
Website: http://www.thorntontomasetti.com/
Author: Paul Fu
Affiliation:
Street Address: 51 Madison Avenue
City: New York
State/County: NY
Zip/Postal Code: 10010
Country: United States of America
Email Address: [email protected]
Fax: 1.917.661.7801
Telephone: 1.917.661.7800
Website: http://www.thorntontomasetti.com/
Author Bios
Yi Zhu, Senior Principal of Thornton Tomasetti, has extensive experience internationally in the
structural analysis, design and review of a variety of building types, including high-rise buildings and
mixed-use complexes, in both steel and concrete. His notable projects include Taipei 101 in Taiwan,
China; the Petronas Towers in Malaysia; Shanghai Tower and the 66-story Plaza 66 in Shanghai,
China. He holds a bachelor’s degree in structural engineering from Tongji University and a master’s
degree in structural engineering from the City College of New York.
Dennis Poon, Vice Chairman at Thornton Tomasetti, has 30 years of experience in the design of
supertall structures and mixed-use buildings worldwide. High on the list of his accomplishments is the
role he played in leading the structural design teams for three of the tallest buildings in China: Wuhan
Greenland Center, Shanghai Tower, and Ping An International Finance Center, currently under
construction. He was named one of the 25 Top Newsmakers of 2010 by Engineering News-Record
magazine for the effort to modernize China’s building codes for supertall structures.
Emmanuel Velivasakis' design experience with materials such as structural steel, cast-in-place
concrete, carbon/glass fiber reinforced plastics, timber, precast and prestressed concrete and masonry,
allows him to participate in the design of various building project types. He is responsible for
managing major projects, such as high-rise buildings, hotels, long-span structures, industrial buildings,
schools, airport terminals, stadia, pedestrian bridges, parking structures, special structures and failure
investigations. His extensive investigation/forensic experience includes numerous types of cases,
ranging from exterior walls, to structural collapses failures and colapses, including emergency
response. He has provided expert witness testimonies for litigation cases involving a variety of issues
in the Structural and Architectural Engineering arena. Mr. Velivasakis also has extensive experience
in seismic design and analysis. He has worked on major projects in severe seismic zones including
US/California, South America, Greece, Turkey, UAE, Guam, Puerto Rico and China and is familiar
with a variety of seismic codes and criteria, as well as performance-based design.
Steve (Qing) Zuo, Vice President at Thornton Tomasetti, has experience in the structural design,
investigation and review of a variety of building types, including high-rise buildings,
commercial/residential, and mix-used complex. He is also well versed in conducting structural
investigations of existing and proposed structures. Steve has been involved in the design of a number
of high-profile projects in China over the past several years, including Shanghai Tower in Shanghai,
Ping An International Financial Center in Shenzhen, and the Shangri-La Hotel in Shenzhen.
Paul Fu, Vice President at Thornton Tomasetti, has 20 years of experience in structural analysis,
design, and review of super-tall buildings and mixed-use structures. He has been involved in major
projects in Asia and the US, including Shanghai Tower, Ping An International Finance Center, Wuhan
Greenland Center, and MGM City Center Block A in Las Vegas. Paul is a licensed professional
engineer in New York. He holds a master’s degree in civil engineering from the University of Toledo
and a bachelor’s degree in civil engineering from Southeast University, Nanjing, China.
Abstract
This paper discusses the structural challenges and solutions of the 632m tall Shanghai Tower. A unique
“Core-Outrigger-Mega Frame” lateral system is used to meet China code requirements. The exterior
perimeter Mega frame provides additional stiffness and strength. A foundation with a 6m thick mat
and fin walls extending from a central core distributes loads to piles constructed with an end grouting
technique to provide high bearing capacity and reduced settlement. The tower crown design
incorporates features for construction efficiency while providing multiple load paths. Performance
Based Design is used to verify tower performance under different seismic hazard levels through non-
linear dynamic time-history analysis.
Keywords
Tall building; Performance-Based Design; Outrigger; Super column; Belt truss, Crown
PROJECT DESCRIPTION
Shanghai Tower in lot Z3-1 is adjacent to Jin Mao Tower, with its pagoda-like gesture to China’s past,
and Shanghai World Financial Center, representing China’s present. Rising as a landmark on the city
skyline to represent the future, the 128-story Shanghai Tower will house Class A office space,
entertainment venues, retail stores, a conference center, a luxury hotel and cultural amenities. The 5-
story deep basement serves retail, MEP and parking spaces (see Figure 1). Occupying a total site area
of about 30,370 m2, the Shanghai Tower has a total gross floor area (GFA) of approximately 573,400
m2 (6.2 million ft2).
Figure 1
The tower structure takes the form of nine cylindrical buildings stacked one atop another, including a
business zone at the bottom podium levels, five office zones, two hotel/apartment zones, and
sightseeing or observation floors at the top. Each zone can be considered an independent city or village
with communal space at an amenity level extending to the outer twisting façade (see Figure 2). The
tower floor plate diameter varies by zone, from 82.2m at Zone 1 to 46.5m at Zone 8 (see Figure 3). The
stacked-zone tower concept within an exterior façade tapering and twisting with height creates a
spectacular architectural design.
Figure 2
Figure 3
GEOTECHNICAL CONDITIONS AND TOWER FOUNDATION
Foundation design is always challenging for tall buildings due to large vertical forces from gravity and
large overturning forces from wind and seismic loading. Site conditions at Shanghai Tower add to the
challenge. Nine layers of sand and clay area alternating to at least 120m below grade. Bedrock is
considered beyond reach for practical construction purposes. Because the top 15m is very soft silty
clay the site for seismic design is considered as Type IV, the most unfavorabe class according to the
China code and roughly comparable to Site Class ‘F’ under the International Building Code (IBC) (see
Table 1).
Table 1- Soil Profile
Soil
Stratum
Succession
Soil Stratum Name Average Soil
Stratum
Thickness
(m)
Average
Distance to
the bottom of
stratum (m)
Saturated
undrained
Shear
Strength
Cu (KPa)
Shear
Wave
velocity
(m/s)
1 Fill 2.2 2.2 - -
2 Silty clay 1.6 3.8 - -
3 Very soft silty clay 5.2 9.0 30 125
4 Mucky clay 7.9 16.9 51 147
51a Clay 3.7 20.6 70 178
51b Silty clay 4.2 24.8 96 215
6 Silty clay 4.2 29.0 115 271
71 Sandy silt + silty
sand
8.0 37.0 - 263
72 Silty sand 27.4 64.4 - 333
73 Silty sand 4.8 69.2 - 377
91 Sandy silt 9.0 78.2 - 399
92-1 Silty sand 11.2 89.4 - 421
92-2 Silty sand 9.6 99.0 - 457
Under the tower footprint a 6m thick mat foundation is supported by 947 piles with one meter in
diameter. The cast-in-place (CIP) concrete piles have end grouting to increase their capacity and
reduce settlement. Under the core and super columns load is concentrated so a staggered pattern pile
layout is used to fit more piles than where using a simple grid arrangement. The 1000-metric ton
capacity piles are effectively 52 to 56 m long and bear at layer 9-2-1, a thick silty sand layer.
Modest soil stiffness offers little ability to distribute gravity loads. Concentrating piles under the core
and super columns is not sufficient by itself to provide reasonably uniform settlement; pile group
effects also play a role. To distribute the tower load more uniformly and thus reduce the overall
settlement and differential settlement, concrete fin walls five stories tall are provided at the basement
levels to engage both core walls and super columns. To handle the large forces being redistributed the
walls include embedded steel plates. These fin walls reduce the maximum predicted settlement by 20 -
30% and greatly reduce differential settlement. Figure 4 shows the settlement contours with and
without fin walls. Tower peak settlement after 5 years is estimated to be 100 to 120mm.
Figure 4
Differential behavior between the tower and surrounding podium also poses structural challenges. The
water table is just 0.5m under grade, while the mat top elevation is at -25.4m. Under the tower
footprint self-weight is sufficient to more than offset buoyancy, but the surrounding podium will have
to resist net uplift forces due to high buoyancy forces. The difference in net foundation loads and the
soft subgrade conditions will cause differential settlement between podium and tower. To reduce the
effects of differential settlement, a delayed-pour strip is provided. The mat reinforcement design must
consider loads and deformations occurring during different construction stages for independent and
combined cases, and include additional reinforcement locally at the interface of tower and podium as
needed.
TOWER LATERAL SYSTEM
The Shanghai Tower lateral system is a “Core-Outriggers-Mega Frame” and it consists of three parts:
Concrete Composite Core, Exterior Mega Frame (Super Columns and Double Belt Trusses), and
Outrigger Trusses (see Figure 5).
Figure 5
The core forms a nine-cell 30m square shape in plan from Zones 1 through 4. The four core corners are
cut back at Zones 5 and 6, and the core becomes a cruciform plan at Zone 7 and 8. The flange
(outermost) wall thickness varies in five steps from 1.2 m to 0.5 m. Interior web wall thickness varies
from 0.9 m to 0.5 m. Embedded wide flange steel columns are provided at the boundary zones, or
stressed core wall corners and ends to both strengthen the core and to provide a clear load path from
outrigger forces into the core. Embedded steel plates are placed in the core walls at the bottom two
zones to enhance wall ductility and permit a reduced wall thickness.
There are eight Super Columns up to Zone 8, and four Diagonal Columns up to Zone 5. Steel columns
embedded in the super columns have areas from 4% to approximately 6% of Super Column plan areas.
The Super Columns work together with eight sets of two-story-high double Belt Trusses to form the
“Exterior Mega Frame” which serves as a second line of defense required by the China Code. Outer
and inner belt trusses are laced together to form a boxed space truss for redundancy and torsional
stiffness. Belts also serve to transfer secondary column gravity loads to the Super Columns.
Six sets of two-story high steel Outrigger Trusses are placed at the MEP floors as shown in Figure 6.
The location and number of outrigger trusses was extensively studied and optimized. The outriggers at
low zones are effective in reducing the building fundamental period, while upper outriggers contribute
more to control of story drifts at upper zones.
Figure 6
The fundamental period of the tower is shown in Table 2 with the first 3 modes representing X-
direction Translation, Y-direction Translation and Torsion, respectively.
Table 2- Building fundamental Period
ETABS
T1 9.05
T2 8.96
T3 5.59
T4 3.31
T5 3.20
T6 2.62
The Outrigger Trusses and Belt Trusses help the structural system to be stiff enough to meet the
stringent story drift limit required by China Code. The story drift curves under the lateral load are
shown in Figure 7. The max story drift is h/505 under resultant wind and h/623 under frequent seismic
load.
Figure 7
TOWER GRAVITY SYSTEM
Typical office floors use a 155 mm thick composite slab (80 mm concrete above a 75 mm deep profile
metal deck) that provides a two-hour fire rating according to laboratory tests. Typical MEP levels and
Amenity levels use 200 to 250 mm thick composite slabs (125 to 175mm above 75 mm metal deck).
Steel perimeter gravity columns have their gravity loads transferred through the belt trusses into the
super columns.
One-story-high radial trusses cantilever at the upper MEP level to support slab areas beyond the super
columns. Those radial trusses also support the exterior facade system, as discussed below.
REDESIGN OF TOWER CROWN
The Shanghai Tower crown is an important part of the building façade system and serves multiple
functions. It houses an 1,100-ton tuned mass damper on top of the central core at L125, a series wind
turbines at the perimeter of L122~L124, cooling towers at L128 surrounding the TMD, and a window
washing machine track along the crown top surface (see Figure 8).
Figure 8
The original design was based on a pretensioned vertical cable net for the outer crown surface to
satisfy architectural criteria. The crown inner surface was carried on radial, outward-sloping
cantilevered ‘fin’ trusses that also supported the cable net upper end loads. The fin trusses stood on
criss-crossed two-way trusses to transition to the core below.
Resisting lateral loads, particularly torsion, required circumferential horizontal trusses to tie the fin
trusses to braced bays. While a perimeter building skin carried on tension rods hanging from the crown
top would have minimal visual interface behind the glass, such a hung system would be costly and
slow to build (see Figure 9 Original Tower Crown 3D view).
Figure 9
The current scheme follows a more conventional approach to cladding support and the structural
system. Instead of suspended pretensioned rods, vertical trusses behind the crown outer face support
the façade and deliver its gravity load directly to L118 below. Lateral loads from wind pressure are
delivered directly to core framing through radial struts. Instead of cantilevered fin trusses, simpler
kicker trusses support the crown inner face while laterally bracing the outer trusses above the tower
roof level at L129. Simple vertically braced bays at three triangle corners work with a horizontal floor
truss at every other floor to help the crown system resist the torsion. This system is more efficient by
providing direct load paths and more conventional fabrication and erection, and more reliable by
having multiple load paths. See Figure 9 Current Tower Crown 3D view and Current Strut Level Floor
Plan.
PERFORMANCE BASED DESIGN
PBD explicitly considers the nonlinearity and ductility of structural members and can be used to
evaluate structure overall behavior and member behaviors under different levels of seismic events. The
PBD procedure of Shanghai Center Tower includes:
Determining performance targets for the overall structure
A PBD model incorporating the nonlinearity of structural components
Determining appropriate ground motion time histories
Performing a nonlinear dynamic time-history analysis
Comparing member deformations and forces with the acceptance criteria
Performance goals for the overall structural system and structural components are summarized in
Table 3.
Seismic Hazard
Level
Frequent
Earthquake Moderate Earthquake Severe Earthquake
Performance
level description
No damage or
negligible damage
Little Damage,
Repairable
Serious Damage, No
Collapse
Structure Behavior
Description
No damage,
structure basically
in elastic range
Allow minor damages ,
structure substantially
retains original strength
and stiffness
Allow serious damage, but
no fracture of major
connection joint; no shear
fracture of super columns
and core walls
Story drift ratio limit h/500; h/2000(
bottom levels) h/200 h/100
Mem
ber
per
form
ance
Core wall Elastic,
Strength design per
code:
- factored seismic
load
- material design
strength
Code-based strength
design
At outrigger floors:
- factored seismic load
- material design
strength
At other floors:
- unfactored seismic load
- material ultimate
strength
Plastic hinge rotation:
θ<IO at at bottom levels
θ<LS at other levels
Shear forces<= ultimate
shear capacity
Link beam
Allow plastic hinge;
Code-based strength
design
Plastic hinge rotation:
θ<LS and <=0.02 rad
Super
column
Elastic,
Code-based strength
design
- factored seismic load
- material design
Plastic hinge rotation:
θ<IO at bottom levels
θ<LS at other levels
Stress in reinf. f > fy but <
fu
Table 3 Performance Target and Acceptance Criteria
strength
Belt truss
Elastic, -factored seismic
load -material design
strength
Elastic ,
steel stress f < fy
Outrigger
Code-based strength
design
-unfactored seismic load
-material ultimate
strength
Plastic deformation:
θ<LS and stress f < fu
Critical
Connections
Elastic, Strength design
per code: factored
seismic load, material
design strength
Special FEM analyses are
required and stress f<= fy
Abaqus and Perform 3D computer programs, widely used for nonlinear analysis, were used to develop and analyze
the mathematical models.
Seven sets of ground acceleration time histories were selected from among available worldwide records to match the
soil profile and were scaled to reflect expected earthquake intensity at the Shanghai Center building site. Each set
included two orthogonal horizontal components plus one vertical component acting simultaneously at a ratio of 1:
0.85: 0.65.
The nonlinear load-deformation characteristics of individual components were modeled according to the constitutive
relation curves of concrete and steel provided in the China code.
A summary from extensive PBD analyses includes the following findings:
For maximum story drift ratios, average values are 1/131(X) and 1/144(Y) (see Figure 10).
Core compressive demand is below ultimate capacity except at a few local points.
Most link beams exhibit plastic deformations within the “Life Safety” limit.
Most outrigger trusses and belt trusses members are still in the elastic range.
Embedded steel elements in super columns and core walls are in the elastic range.
Overall, the tower achieves the requested “Life Safety” performance level.
CONCLUSION
The Shanghai Tower design brought structural engineers a series of challenges: supporting a heavy tower on soft
soils, resisting huge lateral loads while controlling story drifts, supporting the curtain wall panels of a unique
twisting exterior facade disengaged from the main building, and using advanced analysis methods to evaluate
structural performance under different levels of seismic events. Creative structural solutions, such as an Exterior
Mega Frame to enhance tower lateral stiffness and strength, and state-of-the-art analysis approaches from
Performance Based Design were applied to result in an innovative and economical structural design.
ACKNOWLEDGEMENT
We would like to thank Mr. Leonard Martin Joseph, P.E., S.E., Principal of Thornton Tomasetti, Inc, for enhancing
this paper through his thoughtful suggestions.
PROJECT DESIGN TEAM CREDITS
Client: Shanghai Tower Construction & Development Co. LTD
Architect: Gensler
Structural Engineer: Thornton Tomasetti Inc.
MEP Engineer: Cosentini Associates
Local Design Institute: Architectural Design & Research Institute of Tonji University
Wind Engineering Consultant: Rowan Williams Davies and Irwin Inc. (RWDI)
Fire Safety Consultant: Rolf Jensen & Associates (RJA)
REFERENCE
IBC (2006), International building Code , International Code Council.
ASCE-41 (2006), Seismic Rehabilitation of Existing Buildings,
GB50011-2001 (2008 version), Code For Seismic Design of Buildings,
JGJ3 (2002), Technical Specification for Concrete Structures of Tall Buildings,
Shanghai Tower Detailed Reconnaissance Report (Final), September 5, 2008, Shanghai Geotechnical Investigation
& Design Institute Co., Ltd.
Image Captions
Include all figure reference captions in order of appearance in the main body text below using the following format:
Figure 1. Shanghai Tower 3D Rendering View (Source: Gensler)
Figure 2. Shanghai Tower Stacking (Source: Gensler);
Figure 3. Shanghai Tower Typical Floor Plans (Source: Gensler)
Figure 4. Settlement Contours With and Without Fin Walls (Source: Thornton Tomasetti)
Figure 5. Lateral System Components (Source: Thornton Tomasetti)
Figure 6. Exterior Mega Frame and Outriggers (Source: Thornton Tomasetti)
Figure 7. Tower Story Drift under Lateral Load (Source: Thornton Tomasetti)
Figure 8. Tower Crown Section (Source: Gensler)
Figure 9. (Source: Thornton Tomasetti)
Figure 10. Maximum story drifts under different time-histories (Source: Thornton Tomasetti)
Table 1. Soil Profile (Source: Thornton Tomasetti)
Table 2. Building fundamental Period (Source: Thornton Tomasetti)
Table 3. Performance Target and Acceptance Criteria (Source: Thornton Tomasetti)
